Outboard motor-driven hydroplaning boat



Oct. 27, 1953 I E. C. KIEKHAEFER OUTBOARD MOTOR-DRIVEN HYDROPLANING BOAT Filed May 11, 1951' Patented Oct. 27, 1953 UNITED STATES PATENT OFFICE OUTBOARD ,MOTOR-DRIVEN HYDRO- PLAN ING BOAT This invention relates to engine driven boats and particularly to outboard motors for boats which operate on the principle of the hydroplane.

The invention provides an outboard motor having a dirigible propeller which is disposed with respect to the rear of the boat whereby the propeller is entirely submerged while the boat is being driven at less than a planing speed and as the boat approaches the planing speed the propeller is withdrawn partially from the water to operate as a surface-pitch propeller.

The principal object of the invention is tosecure in a single propeller the thrust necessary to start the boat and reach the planing speed and to accommodate thereafter the high rotational speeds at which the maximum output of the engine is obtained to drive the boat at higher speeds.

A more particular object of the invention is to utilize to advantage the tendency of the boat to heel as the water speed of the boat increases and the reaction of the water striking the underside of the boat becomes gradually effective to support the boat irrespective of its normal dis placement.

A further object is to eliminate the need of devices for raising and lowering of the propeller relative to the boat during operation.

These and other objects and advantages will be more fully set forth in the following description of a preferred embodiment of the invention as illustrated in the accompanying drawing.

In the drawing:

Figure 1 is a side elevation of the outboard motor-driven boat showing the motor and boat as the latter approaches a planing speed;

Fig. 2 is a view similar to Figure 1 showing the motor and boat in the position in which the boat is supported at planing speeds; and

Fig. 3 is a rear view of the motor and boat as shown in Fig. 2.

The outboard motor I shown in the drawings includes the power head 2, preferably a two-cycle internal-combustion engine of low weight per horsepower ratio, and the housing 3 which supports the power head at the upper end of the housing.

The streamlined gear case 4 is secured to the lower end of housing 3 and carries the propeller 5 rearwardly thereof.

Propeller 5 is driven by the engine of power head 2 through gear case 4 and is disposed immediately beneath the anti-cavitation plate 6 which extends generally rearwardly of the motor and horizontally over the propeller.

The clamp bracket assembly I is pivotallyconnected to housing 3. to support the latter for pivotal movement of power head 2, housing 3 and the gear case 4 for turning movement as a unit on a vertical axis to turn propeller 5 and eifect the directional control of the boat 8.

Boat 8 includes the transom 9 which extends across the rear of the boat. The underside of the boat preferably comprises forward and rear planing surfaces l0 and II respectively and is stepped as at I2 at approximately the center of ravity of the boat.

Bracket assembly I is adapted to be secured over the upper end of the transom 9 of the boat and supports the motor with propeller 5 directly rearwardly of the rear planing surface H of the boat 8 and in a given relation to the diameter of the propeller.

According to the invention propeller 5 is of a diameter generally less than the distance between the propeller and the trailing edge of the rear planing surface H and is disposed with its rotational axis adjacent to or just below the horizontal level of the rear planing surface II.

In the operation of motor I in driving boat 8 at a planing speed, the dynamic reaction of the water to the planing surfaces l0 and l l supports the boat independently of its normal displacement and with. the boat disposed at the general: level of the two planing surfaces. In such a position, propeller 5 is partially out of water to operate as a surface-pitch propeller wherein the blades l3 of the propeller successively enter the Water at a given angle according to their pitch.

In the surface-pitch position the propeller is particularly adapted to turn at the high rota.- tional speeds of the engine of power head 2.

In bringing the boat up to a planing speed, a considerable propeller thrust is required before the boat reaches the required speed. The propeller, which is subject to cavitation at a highrotational speed, must be designed accordingly to provide at least the minimum thrust neces sary at a relatively low water speed.

Assuming the same weight distribution of the load carried in the boat, the rear of the boat lowers and the bow lifts out of the water as the planing speed is approached. According to the invention, propeller 5 is disposed so as to be completely submerged in the water swell which trails the boat as shown in Figure 1, until the planing speed is reached and the boat levels to the position shown. in Fig. 2.

By providing for the full submergence of the propeller at lower speeds a smaller diameter propeller of greater pitch can be employed with a motor of a given horsepower tobring the boat up to a planing speed and will operate efiieiently at higher rotational speeds as the boat approaches a maximum speed. The period of full. submergence provided to reach the planing speed. corresponds with the increased drag of the boat until such planing speed is reached.

Various embodiments of the invention may be employed within the scope of the following claim.

I claim:

In combination, a boat having a given displacement at low speeds and having planing surfaces supporting the boat as a hydroplane above a critical speed, a dirigible outboard motor unit secured to the rear end of said boat to drive the same and having a forward thrust propeller disposed rearwardly from the trailing edge of the rear planing surface of the boat a distance at least as great as the diameter of the propeller and extending to a depth beneath said planing surface approximately equal to the radius of the propeller whereby said propeller is wholly submerged during operation below said critical speed to operate with 'maximum thrust and the full blade area and is partially submerged for normal operation at planing speeds, said propeller being dirigible with the motor and adapted to maintain the directional control of the boat by the lowermost blades of the propeller.

ELMER c. KIEKI-IAEFER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,044,176 Hickman Nov. 12, 1912: 1,226,400 Smith May 15, 1917 1,335,130 Hooke July 19, 1921 2,096,457 Irgens Oct. 19, 1937 2,337,376 De Micelis Dec. 21, 1943 2,442,728 Kziekhaefer June 1, 1948 

